PCM1841-Q1: How are the 4 inputs handled when I2S is selected?

Part Number: PCM1841-Q1

Tool/software:

When the I2S output is selected (which supports 2-channels) how are the 4 inputs handled? Do they mix (e.g. 1 and 3 mixed to left and 2 and 4 mix to right) or are 3 and 4 ignored completely. Is there any MUX function to tell the chip which inputs to route to the left and right I2S channels?

-Many Thanks in Advance.